Basically whats occurring is that once the vehicle is under load, a strange (almost pre set) develops from the engine bay almost directly in front of the steering wheel.Click the Youtube link to see what it sounds like, have to listen carefully.https://youtu.be/coQymne6EZo

I'm assuming there's no warning lights on dash. How long have the exhaust and intake been on for? Is it possible one or the other (especially the intake based on where you say the noise is coming from) has become a bit loose?You say it happens under load, but is it always the same gear or same rpm?Is the car still running well or does it feel down on power?

1. Take a look at the black plastic tube that covers the fuel lines running down the left side of the engine just below the coolant water tank, on my car the mount at the top snapped leaving it to rattle against a metal pipe along the side of the engine - few cable ties and some adhesive cable tie mounts along the plastic cover did the job.

2. The bonnet - few tweaks of the rubber stoppers under the bonnet will sort that one out

3. (may not apply to you) - The mounts on the first part of the intake up against the radiator snapped on mine leaving that to rattle a little - apparently my rear engine mount is a little worn which causes the engine to pull it off when it rotates a bit more than it should on acceleration.